Efficient Photocatalytic Hydrogen Production over Rh-Doped Inverse Spinel Zn2TiO4

Introducing foreign elements is an appealing means to endow wide band gap semiconductors with visible-light responses. Here, we investigated a series of Rh-doped Zn2TiO4 as water reduction photocatalysts. Our results show that Rh doping is effective to improve the visible-light response as well as surface hydrophilicity of Zn2TiO4. Efficient photocatalytic hydrogen evolution was observed after Rh doping and was found to be compositional dependent. The best performance was recorded for sample Zn2Ti0.96Rh0.04O4, with an apparent quantum efficiency of approximate to 0.74% under full-range irradiation (lambda >= 250 nm) and approximate to 0.25% under visible-light irradiation (lambda >= 420 nm). The light absorption and surface hydrophilicity are likely the controlling factors for the better activity. Theoretical calculations suggest that Rh doping is responsible for a band gap reduction and is due to a newly formed valence band composed mainly of Rh 4d orbitals at the top of the original valence band. The visible-light activity can be attributed to the electron excitations from this new valence band to the conduction band.